Computer systems are pervasive in industrialized societies, and include everything from small handheld electronic devices, such as personal data assistants and cellular telephones, to application-specific electronic devices, such as set-top boxes, digital cameras, and other consumer electronics, to medium-sized mobile systems such as notebook, sub-notebook and tablet computers, to desktop systems, workstations and servers.
In recent years there have been many advances in semiconductor technology that have resulted in the development of improved electronic devices having integrated circuits (ICs) operating at higher frequencies and supporting additional and/or enhanced features. While these advances have enabled hardware manufacturers to design and build faster and more sophisticated computer systems, the advances have also tended to bring the disadvantage of higher power consumption, particularly for battery-powered computer systems.
A number of techniques are known for reducing the power consumption in computer systems. For example, the Advanced Configuration and Power Interface (ACPI) Specification (Rev. 2.0c, Aug. 25, 2003) sets forth information about how to reduce the dynamic power consumption of portable and other computer systems. With respect to processors used in computer systems, four processor power consumption modes (C0, C1, C2 and C3) are defined in the ACPI Specification. For example, when a processor is executing instructions, it is in the C0 mode. The C0 mode is a high power consumption mode. When the processor is not executing instructions, it may be placed in one of the low power consumption modes C1, C2 or C3. An operating system (OS) in the computer system may dynamically transition the idle processor into the appropriate low power consumption mode.
The C1 power mode is the processor power-saving mode with the lowest latency. The C2 power mode offers improved power savings over the C1 power mode. In the C2 power mode, the processor is still able to maintain the context of the system caches. The C3 power mode offers still lower power consumption compared to the C1 and C2 power modes, but has higher exit latency than the C2 and C1 power modes.
While the reduced power consumption modes defined by the ACPI Specification and known techniques have many advantages, there is a continuing need to further reduce power consumption of computer systems. That need has been heightened by the migration of IC technology to sub-micron line widths, which has resulted in increasing possibilities for current leakage in ICs even during idle conditions.